1. Series with respect to the Walsh systems and their generalizations;Balasov;J. Soviet Math.,1973
2. Walsh Functions and their Applications;Beauchamp,1975
3. De la Vallée Poussin J., Lecons sur l'approximation des fonctions d'une variable réelle, Paris, 1919.
4. On the Walsh functions;Fine;Trans. Amer. Math. Soc.,1949